Merge branch 'issue-61' into 'master'

Dockerfile: add yarn.lock before running `yarn install`

Closes #61

See merge request !37

Dockerfile

@@ -3,6 +3,7 @@ FROM node:8-alpine
 WORKDIR /usr/src/app/hublot
 
 COPY package.json .
+COPY yarn.lock .
 
 RUN yarn install